1. Field of the Invention
The present invention relates to a workpiece conveying apparatus for use in conjunction with a working machine such as, for example, a press. The conveying apparatus is used when the workpiece (i.e., an article to be worked) is loaded into or unloaded from a die or jig of the press, conveyed from one step to a subsequent step or aligned.
2. Description of the Prior Art
In a working machine such as, for example, a press, a conveying apparatus is used to load or unload a workpiece into or from a die or jig of the working machine. Conveying apparatus of the prior art is usually constructed by combining a mechanism for moving the workpiece in a horizontal direction with a mechanism for moving the workpiece in a vertical direction. A conventional workpiece conveying apparatus is usually equipped with a drive source separate from that of the associated working machine. Therefore, it cannot have its work conveying operation accurately timed to be synchronous with the opening and closing operations of the working machine. Instead, it performs with so-called "intermittent operation", in which the opening operation of the working machine is elongated, if a danger of interference is taken into consideration. As a result, the working machine has an increased number of starts and stops which leads to an increase in fatigue and damage.
In recent years, there has been developed a workpiece conveying apparatus which eliminates the aforementioned operational disadvantage by using a drive source common to the conveying apparatus and the working machine. However, even their recently developed conveying apparatus is unsatisfactory, as will be discussed further on.
The common drive source runs the working machine continuously while the conveying apparatus and the working machine having their respective operations time coordinated. The conveying apparatus of the kind developed will be explained with reference to FIGS. 16 to 20 (all PRIOR ART) in connection with an embodiment in which it is applied to a press machine. Indicated at reference numeral 51 is a drive source which is made rotatable in synchronism with a motor for driving an upper die 68. The rotation of the drive source is reduced through a belt 51a by a reduction mechanism 52 to that the reduced rotations are transmitted to a sector gear 54 through a piston rod 53 which is connected to a crankshaft of the reduction mechanism 52. A rocking lever 57 is fixed to a gear 56, which is made rotatable in meshing engagement with the arcuate teethed portion 55 of the sector gear 54 enabled to reciprocatively rock at a predetermined angle by that piston rod 53, so that it reciprocatively rocks together with the sector gear 54. To the leading end of that rocking lever 57, there is connected rotatably a slider arm 58 which constitutes a parallel link mechanism together with a slider link 59, a lower side link 60 and a sub arm 61. The slider link 59 is non-rotationally but slidably fitted in a vertically extending slider rail 62 so that the lower side link 60 of the aforementioned parallel link mechanism may be moved while keeping its horizontal position by the reciprocal rocking motions of the rocking lever 57. Indicated at numeral 64 is a work holder which is equipped with a sucking cup 65 at its leading end. Here, if the piston rod 53 is moved up and down, the locus drawn by a link pin 63 can be so set by the rocking angle of the reciprocal rocking motions of the rocking level 57 as is indicated at letter A in FIG. 17. Reference numerals 66 and 67 appearing in FIG. 16 indicate that locus and the position of the sucking cup after movement, respectively.
According to the conveying apparatus thus constructed, the locus of the working motion drawn by the sucking cup 65 follows that of the returning motion drawn during the returning action. Here, the explanation to be made is directed to the case wherein the work holder conveys the work in loading, for example. As shown in FIG. 8 (PRIOR ART), when the upper die 68 is at the top dead point of its stroke H, a workpiece W is conveyed in by the sucking cup 67, and only this cup 67 returns. At this time, the sucking cup 67 comes out of the die along the same locus as that traversed during loading. Despite this fact, the vertical stroke H of sucking cup 65 has to be made considerably large in the vertical direction in view of the fact that the workpiece is usually set in the die. Moreover, during the time period from the instant when the upper die 68 reaches the top dead point to the instant when the die 68 begins to move down for a working operation, upper die 68 has to be temporarily stopped, until the work holder comes in the die and leaves the die, so as to avoid interference with the work holder, thus causing an operational disadvantage in that working efficiency is degraded. FIG. 1 (PRIOR ART) is a diagram showing the timing of the upper die and indicates that the working machine has a stand-by time at its top dead point. On the other hand, FIG. 20 (PRIOR ART) is a cycle diagram in which the displacement of the die is plotted against the crank angle of the working machine.